You’d be surprised how many startups come to us with excellent connected device concepts that have failed under routine, predictable environmental stresses.
Ruggedizing IoT opens entrepreneurs up to a whole new host of applications — in industrial IoT (IIoT), defense, agriculture, oil and gas, unmanned systems, smart cities, and utilities — but special care must be taken when you’re going into a rugged environment.
Water, vibration, dust, temperature extremes, and salt threaten every electronic device in the great outdoors, and IoT devices have the additional challenge of keeping their communications kit in working order. Many startups go with off-the-shelf, consumer, electronics-based modules that work fine when they’re operating at low vibration with low humidity, but they don’t cut it at high temperatures.
Off-the-shelf modules work fine at low vibration with low humidity, but they don’t cut it at high temperatures.
When you design a product that needs to survive outside, underground, or in space, it is vital to figure out the specifications first. Where is it going, and what will that environment hit it with? A device for down hole on a drilling rig must have all its components able to handle -40 to +225 Celsius, and be resistant to dust intrusion and salt water under pressure. By contrast, the WiFi module in a tablet is only spec’d for 0-70 Celsius and can’t take much moisture, dust, or vibration.
We recently wrote about creative solutions for ruggedizing IoT to survive in all sorts of extreme conditions — because if your device fails in the field, it will likely cost more to send a truck out to service it and/or replace it than the device or data was ever worth. IoT devices are supposed to save money, increase profitability, and optimize ease of use. That post left me wanting a more zoomed-in, components-level discussion about ruggedizing a device from the inside out:
Work From the Inside Out
The best way to think about the design process for electronic products is to work from the inside out. Always start with your components, and consider the different stressors they’ll encounter. Temperature is usually the most common and important, because it can damage electronics in several different ways. Mechanical stresses are often overlooked, as well, and can cause a range of failures.
Integrated Circuits (the Electronic Guts)
First, consider how your integrated circuits — the electronic semiconductor parts of your device — will be packaged and mounted. Always check the operating temperature range of the part you intend to include in your design, and the cost and availability of that particular part number. Once you make sure you can actually get a part that will work for your application environment, take a look at how the parts are packaged again.
Chip scale packages can be very small and designed to be soldered directly onto the printed circuit board. This can make your device very small and flat, and it’s how many new chips are built today. They are smaller, and less expensive for the manufacturer to produce, but they’re also more vulnerable to temperature and physical stresses.
Temperature cycling can be overlooked — the parts on the board, and the parts themselves, contract and expand under changes in temperature at different rates. If your device gets too hot or cold and the board warps, the solder can crack and the chips will become only intermittently connected — or worse, fall off. There are ways to avoid this: You can either make your PC board thicker and make sure your chips are very tiny, or you can select a different kind of packaging for your chips.
Make your choice based not just on the latest functionality you can get in a chip, but also on how its packaging will impact your design later on.
Older style surface-mount packaging — quad flat packs (QFP), SOICS, SOTs, and others — tend to be more robust, because they have metal ‘gull wings’ as the leads attaching to the PCB. These wings act as little springs, flexing with the board and giving the device a great deal more temperature and vibration protection. The problem is, if you haven’t chosen a device during the design process that has this type of packaging, it can have impacts much further down the road in terms of managing reliability.
Not all chips have a range of options available for temperature ranges or physical conditions that will work with your requirements. Make your choice based not just on the latest functionality you can get in a chip, but also on how its packaging will impact your design later on.
Passive Components: Capacitors, Inductors, and Antennas
Next, check out how components such as capacitors, inductors and your antennas are attached. Surface mount capacitors, in particular, are more delicate than often thought; they are made of a brittle ceramic. Minor flexing of the part can cause cracking in the layers that make up the capacitor, causing intermittent failures that can be hard to track down. If you have concerns about the board flexing — under physical stress or temperature changes — try using components that have flex mount terminations. They can be a bit more expensive and harder to find, but can withstand rougher conditions.
Warping and cracking aren’t the only problems components encounter during temperature extremes. Inductors can change values at the edges of their temperature range or operational frequency, for example. Read the data sheets for all components — even the ones that seem to be a given — and understand what happens at the extreme ranges of what your product can experience.
At Bresslergroup we run simulations at those extremes before we build the prototype. And you should do this, too, to avoid the expense and heartbreak when your new IoT product dies after being left outside in Arizona on a July afternoon. We use SPICE for analog circuits, add in Altium and other tools for digital, and have a multiphysics tools to simulate magnetic devices.
Special Considerations for Magnets and Inductors
Magnets and inductors are affected by temperature? Yes. By impact, too. There’s a point called the Curie temperature at which a magnet’s molecules bounce around violently enough that they’re no longer aligned. They don’t melt at the Curie temp, but they lose their magnetism until they cool down. The same thing happens when you overheat an inductor. It loses its mojo. Inductors and magnets are intrinsic to power supply and often to antennas, so if the value of your part starts to drift, your IoT device can no longer talk to the world. Do your homework, and keep your antenna tuned!
User Controls: Connectors, Switches, and Buttons
Last but not least, don’t forget about connectors, switches, and buttons. User controls are part of almost every device. These interfaces are your device’s connection to the outside world, which means they’re going to get abused with dust, moisture, pressure, and flexing. Connectors see significant pressure and torque from cables and mate/de-mate forces. Opt for parts that have a means of transferring forces to something other than fragile surface-mount solder joints. Parts with stakes through the board or screw mounts to the device housing are less likely to fail.
Connectors are also a good place to think about water. The spots where the printed circuit board connects to the outside are the weak points where water and dust can intrude and attack the components. Some interfaces, such as sensors that use light or pressure, can be sealed inside a protective membrane such as molded silicone or GoreTex that’s translucent or pressure sensitive.
Note that ruggedized connectors can get pricey fast. A simple connector that costs less than a buck for consumer electronics can easily cost hundreds of dollars with high temperature range and vibration specification. A waterproof, properly sealed military-spec connector can easily cost $35. When in doubt as to which connectors we could use, we check with the IPC, an assembly standards body that issues industrial and auto standards for electronic connectors.
Protecting against water can sometimes be simple. For example, you can conformal coat the entire board in sealant after it’s assembled. This is a great way to protect against dust and condensation in high humidity environments. But it can add cost and make repairs difficult if board changes need to made.
If a product has to deal with significant physical stress as well as water intrusion, you can pot it. Potting, or encasing the board in epoxy, makes the board very robust and waterproof. However, there are downsides; radio signals can be affected by the potting, and wide swings in temperature or sharp acceleration can crack the epoxy — and take the board with it. If vibration is a bigger threat than temperature, you could pick a flexible, foaming potting compound that protects the board the way a bicycle helmet protects your head.
Just keep in mind that epoxy is an insulator, which means it has an electrical permittivity that could detune your IoT device’s WiFi or Bluetooth antenna. And some thermally transparent potting compounds have metal in them that can also mess with your antenna. There are specialized potting compounds for RF applications, and those may be the best choice. As always, do your research.
Even if you’re not worried about water getting inside your device, you might need to worry about water on the outside. Humidity can mess with touch screens, as can snow. If the touch screen is good for cold and humidity, it probably also needs to contend with gloved fingers. If that’s the case, make sure the screen can use projected capacitance, or consider resistive or glass-deflection options. Lastly, make sure your device display has enough brightness and contrast for outdoor applications.
Spend Time and Money Upfront
Figuring out where your ruggedized IoT device is going to spend its time, and the environmental stressors it will encounter, is the single most important thing you will do during product development. And spending a little more up front on simulations and properly specified components will save you a bundle later on, and avoid costly redesigns.
Nothing beats good planning.
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